The prior art inner spiral ribbed tube is described in U.S. Pat. No. 4,705,103 issued No. 10, 1987. Related prior art references include U.S. Pat. Nos.
______________________________________ 2,167,933, issued February 8, 1938, 3,273,599, issued September 20, 1966, 3,753,364, issued August 21, 1973, 4,118,944, issued October 10, 1978, 4,154,296, issued May 15, 1979, 4,658,892, issued April 21, 1987, and 4,660,630, issued April 28, 1987, and ______________________________________
also include a related prior art reference paper, which was presented in Atlanta, Ga., USA, at the ITA Meeting, that was held on Oct. 15, 1984, and which is entitled "Internally Grooved Tubes for Air Conditioners", and which explains the prior art method of manufacture.
The prior art inner spiral ribbed tube includes a cylindrical wall having an inner surface, said inner surface having a plurality of inner spiral ribs, said inner spiral ribs each having a spiral angle formed by a tangent to a point on the rib and a longitudinal line through the point and parallel to an elongate axis of the tube, said spiral angle measuring about in the range of 0 degrees to 35 degrees.
One problem with the prior art inner spiral ribbed tube is that the size of its spiral angle is limited. Also, the ratio of rib height to number of ribs is limited, which affects the fluid flow and heat transfer parameters of the tube.
The prior art method of making a heat exchanger for use as a refrigerator condenser or for use as a refrigerator evaporator includes the steps of: making a coil of inner spiral ribbed tube having a rib spiral angle of about 18 degrees; uncoiling and feeding the inner spiral ribbed tube along an elongate tube axis.
The prior art method of making an inner spiral ribbed tube includes the steps of: positioning a grooved rotary mandrel mounted on an elongate tie rod within a plain surfaced tube having an elongate axis; positioning an outer annular member having a plurality of rotary bearing members opposite the rotary mandrel; applying radically inward forces from the rotary bearing members through the tube to the rotary mandrel and swaging and forming a spiral ribbed tube; and pulling the spiral ribbed tube away from the rotary mandrel along the elongate axis.
One problem with the prior art method of making an inner spiral ribbed tube is that the spiral angle has to be low enough, such as about 18 degrees, to prevent the tube from being held by the rotary mandrel, resulting in a breaking of the tube. Another problem is that the friction created limits the height of the rib on the inside of the tube; and limits the number of ribs per unit tube length that can be made. A further problem is that the operation is very slow in three part speed and thus high in production costs. Tooling is costly and limited in tool life.